In my code I subscribe to an event that happens on a different thread. Every time this event happens, I receive an string that is posted to the observable collection:

    Dispatcher currentDispatcher = Dispatcher.CurrentDispatcher;
    var SerialLog = new ObservableCollection<string>();

    private void hitStation_RawCommandSent(object sender, StringEventArgs e)
    {
        string command = e.Value.Replace("\r\n", "");
        Action dispatchAction = () => SerialLog.Add(command);
        currentDispatcher.BeginInvoke(dispatchAction, DispatcherPriority.Render);
    }

The code below is in my view model (could be in the code behind, it doesn't matter in this case). When I call "hitstation.PrepareHit", the event above gets called a couple times, then I wait and call "hitStation.HitBall", and the event above gets called a couple more times.

    private void HitBall()
    {
        try
        {
            try
            {
                Mouse.OverrideCursor = Cursors.Wait;

                //prepare hit
                hitStation.PrepareHit(hitSpeed);

                Thread.Wait(1000);
                PlayWarning();

                //hit
                hitStation.HitBall(hitSpeed);
            }
            catch (TimeoutException ex)
            {
                MessageBox.Show("Timeout hitting ball: " + ex.Message);
            }
        }
        finally
        {
            Mouse.OverrideCursor = null;
        }
    }

The problem I'm having is that the ListBox that is bound to my SerialLog gets updated only when the HitBall method finishes. I was expecting seeing a bunch of updates from the PrepareHit, a pause and then a bunch more updates from the HitBall.

I've tried a couple of DispatcherPriority arguments, but they don't seem to have any effect.